The present invention relates to an arrangement at rotating shafts, which comprises a wheel fixedly mounted to the shaft, which wheel rotates in a housing surrounding the wheel, an essentially pipe-shaped element surrounding the shaft, and with essentially axially sealing surfaces provided sealing device between the pipe-shaped element and the wheel and a passage in the housing for the shaft with a sealing device, which seals against the pipe-shaped element.
Sealing arrangements of the kind described above are used on several various kinds of machines. An especially important field of use is fans and pumps of the centrifugal type.
The invention has been found to be especially valuable in those cases, when a pump impeller is mounted on a conical shaft end. This is because it has been found at the machining of the centre hole for the shaft end, that a very small difference in machining depth makes a great difference in the axial position of the pump impeller, when it is mounted. Previously known pumps of this type comprise a pipe-shaped element in the shape of a wear or shaft sleeve surrounding the pump shaft and a stuffing box mounted on the pump housing, which seals against the outside of the wear sleeve. In order not to get leakage between the wear sleeve and the shaft, there is also at this place required a sealing arrangement, which suitably is placed between the end surface of the wear sleeve and the pump impeller. This seal usually is a ring of resilient material placed in a slot between the sleeve and the pump impeller.
However, it has been found that in those cases when the distance between the end surface on the wear sleeve and the pump impeller varies within rather wide limits, so will such a resilient ring not always give satisfactory sealing effect. This is because a ring, which is so soft, that it is always compressed at mounting of the wheel, cannot give a perfect seal at high pressure differences if said slot is wide. If a sealing ring made of harder material is used, one cannot be sure, that the pump impeller has been mounted solidly abutting against the shaft end and not against the sealing ring. More narrow size tolerances for the pump impeller would on the other side cause great costs because of an increased number of cessations during machining. The use of sealing rings of different widths will certainly cause errors at the mounting because the right size of sealing ring is not used.
It is previously known to arrange a threaded portion on a pump shaft for tightening a nut or a threaded shaft sleeve. This embodiment has several disadvantages. Should any damage occur to the thread, this will cause substantial spare part costs, because the entire shaft must be replaced. When the threaded portion is repaired, for instance rethreading or loosening of a nut, which is stuck by rust, the entire pump must be dismantled and the shaft removed from the bearing housing. In both cases, there may also be great down-time costs because of lost production. The thread itself constitutes an indication of fracture, which may cause fatigue failure of the shaft. The thread itself is not protected and may easily be damaged during storage and transport. Such an arrangement with a threaded shaft cannot be installed in an existing pump without a great interference in the pump and exchange of the shaft.